Impact air driven tool

ABSTRACT

An impact air driven tool. A cylinder has a piston slidable therein for striking a chisel, the chisel being operatively supported by a chisel holder secured to one end of said cylinder. A valve member is mounted within a valve casing and is reciprocated within said casing by piston operating air supplied into an upper cylinder cavity above the uppermost end surface of the piston and a lower cylinder cavity beneath the lowermost end surface of the piston. A limiting valve is provided and is operated by a variation of the amount of air within said cylinder for change-over of supply of said piston operating air to said valve member. A throttle valve is disposed in an intermediate portion of a passage through which compressed air for shifting the valve member from the advanced position to the original position is supplied from the limiting valve to the valve member. The throttle valve controls the flow of air to the valve member and thereby adjusts the duration of the piston resting phase during which the valve member is shifted.

United States Patent Terada IMPACT AIR DRIVEN TOOL inventor: HiromuTerada, lkoma, Japan Assignee: Nippon Pneumatic Manufacturing CompanyLimited, Osaka City, Osaka Prefecture, Japan Filed: May 21, 1970 Appl.No.: 39,390

[30] Foreign Application Priority Data Feb. 19, 1970 Japan ..45/ 14404Feb. 19, i970 Japan ..45/ 14405 US. Cl ..173/137, 173/138 Int. Cl ..E2lb1/00, 825d 9/00 Field of Search ..173/135, 137, 138

[56] References Cited UNITED STATES PATENTS 8/1966 Cooley et a1..l73/138 X 8/1939 Holloway ..173/ 137 X 3/1950 Horvath 173/137 X 6/1964Zinkiewicz.... 173/137 X 6/1966 Leavell 173/137 X [57] ABSTRACT Animpact air driven tool. A cylinder has a piston slidable therein forstriking a chisel, the chisel being operatively supported by a chiselholder secured to one end of said cylindenA valve member is mountedwithin a valve casing and is reciprocated within said casing by pistonoperating air supplied into an upper cylinder cavity above the uppermostend surface of the piston and a lower cylinder cavity beneath thelowermost end surface of the piston. A limiting valve 1 is provided andis operated by a variation of the amount of air within said cylinder forchange-over of 'supply of said piston operating air to said valvemember. A throttle valve is disposed in an intermediate portion of apassage through which compressed air for shifting the valve member fromthe advanced position to the original position is supplied.

from the limitingvalve to the valve member. The throttle valve controlsthe flow of .air to the valve member and thereby adjusts the duration ofthe piston resting phase during which the valve member is shifted.

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- INVENTOR ATTORNEYS IMPACT AIR DRIVEN TOOL The present inventionrelates to an impact air driven tool utilizing compressed air forproducing destructive forces.

The present invention has in its object to provide an impact air driventool with which, as compared with one exemplary type of conventionalimpact air driven tools, a relatively greater value of striking energyper piston stroke can be obtained.

Another object of the present invention is to provide an improved impactair driven tool wherein the number of piston strokes can be varied fromthe zero value to the maximum possible value as desired so that theoptimum value can be selected to suit to the capacity of a compressor instock in case of said tool of the present invention being in effectconnected with said compressor in stock.

These and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withpreferred embodiments thereof with reference to the attached drawings,in which:

FIG. 1 is a longitudinal sectional view of one embodiment of the presentinvention with a portion being broken away,

FIG. 2 is a cross-sectional view of a control valve mechanism in saidembodiment of the present inventron,

FIG. 3 is a longitudinal sectional view of a throttle valve portion, onan enlarged scale, employed in the embodiment shown in FIG. 1,

FIG. 4 is a longitudinal sectional view, on an enlarged scale, of arapid exhaust valve portion employed in the embodiment shown in FIG. 1,

FIG. 5 is alongitudinal sectional view of a modified embodiment of thepresent invention with a portion being broken away,

FIG. 6 is a cross-sectional view of a control valve mechanism employedin said modified embodiment shown in FIG. 5,

FIG. 7 is a longitudinal sectional view, on an enlarged scale, of athrottle valve portion employed in the modified embodiment shown in FIG.5,

FIG. 8 is a longitudinal sectional view, on an enlarged scale, of arapid exhaust valve portion employed in the modified embodiment shown inFIG. 5, and

FIG. 9 is a longitudinal sectional view, on an enlarged scale, of acheck valve portion employed in the modified embodiment shown in FIG. 5.

As illustrated in the attached drawings, the improved impact air driventool according to the present invention basically comprises a cylinderunit, a piston unit, a chisel unit, and a control valve unit forcontrolling the flow of compressed air supplied to said cylinder unit.

Referring now to FIG. 1 through FIG. 4 in which one preferred embodimentof the present invention is shown, reference numeral 11 represents acylinder, 12 represents a top plate secured to an upper end of saidcylinder, 13 represents a chisel holder secured to a lower end of saidcylinder, 14 represents a chisel and 15 represents a piston slidablyreceived in said cylinder.

end of said nipple 19 remote from said supply port 18 is rigidlyconnected with an elbow 20 to which a tubular hose connected from asuitable compressor means may be connected.

The valve casing 16 is secured at its right-hand side as viewed fromFIG. 2 with a plate member 21 formed therein with a passage 22communicating with a righthand opening 24 of a valve chamber 23.

The valve casing 16 is also provided therein with a limiting valvechamber 26 slidably receiving a limiting valve therein and with a valvechamber 28 having therein a tubular check valve 27 biased by a spring tothe left within said valve chamber 28. This valve chamber 28 is formedat its outer peripheral surface with a tubular gap 29 and at itsleft-hand portion with a passage 31 communicating with said passage 22.Thus, said check valve 27 acts to permit the flow of air from thepassage 31 to the gap 29, but to restrict said flow from the gap 29 tosaid passage 31.

The plate member 21 is also formed therein with an adjustable needlevalve in the form of a throttle valve 32 situated between a passage 33and a passage 34, which are also formed within the plate member 21, forregulating the flow of air passing between said passages 33 and 34. Thepassage 33 is communicated with the valve chamber 28 while the passage34 is communicated with the gap 29.

The valve body 17 is formed at its right-hand portion with an enlargeddiameter portion. 35 having a recess at its right-hand extremity in theaxial direction thereof, so that when said valve body 17 is moved to theright an annular groove 36 on the inner peripheral surface of the valvechamber 23 can be closed by said enlarged diameter portion 35 while,when said valve body 17 is moved to the left, said annular groove 36commences to communicate with the opening 24 through a righthand portionof said chamber 23 and also with said gap 29.

The valve body 17 is formed about its intermediate portion with areduced diameter portion 40 which, upon movement of the valve body 17 tothe right, acts to communicate between annular grooves 41 and 42 formedon the inner peripheral surface of the valve chamber 23 at a positionaround said reduced diameter portion 40. This annular groove 41 isdirectly communicated with an exhaust port 43 formed in the valve casing16 and the annular groove 42 is directly communicated with a passage 44formed as shown in FIG. 1, in a wall portion of the cylinder 1 l.

The valve chamber 23 is also formed on its inner peripheral surface at aleft-hand portion next to the annular groove 41 with an annular groove45 which.may be communicated with the annular groove 41 through saidreduced diameter portion 40 when the valve body 17 is situated to theleft, but blocked of its communication therewith when the valve body 17is situated to the right. This annular groove 45 is directlycommunicated with a passage 46 open to the interior of the cylinder 11at a position below an opening of the passage 39, as shown in FIG. 1.

The limiting valve 25 is formed at its intermediate portion with areduced diameter portion 47 which, upon movement of said valve 25 to theright, acts to communicate between passages 48 and 49 formed on theinner peripheral surface of the valve chamber 26.

This passage 48 is directly communicated with the gap 29 and the passage49 is directly communicated with the annular groove 37.

The valve chamber 26 is also formed in its peripheral wall at a positionabout the right-hand extremity of the limiting valve 47 with a passage50 and about a lefthand portion of the limiting valve 47 with a passage51 and a passage 52. The passage 50 is communicated with the annulargroove 38 by means of the common passage 39 which is in turn open to theinterior of the cylinder 11. The passage 51 is communicated with theannular groove 45 by means of the common passage 46 which is in turnopen to the interior of said cylinder 11. The passage 52 may becommunicated with the passage 48 through the reduced diameter portion 47to permit the flow of air to an exhaust port 53 when the limiting valve25 is moved to the left.

Reference numeral 54 represents a rapid exhaust valve casing secured toan intermediate portion of the cylinder 11. As shown particularly inFIG. 4, this rapid exhaust valve casing 54 is formed with a ventilatingport 55 directly communicated with a ventilating hole 68 formed in thewall of the cylinder 11. Within said valve casing 54, a valve chamber 59is formed for slidably receiving therein a valve member 56 capable ofclosing and opening the ventilating port 55. It should, however, benoted that the valve member 56 is formed with an auxiliary valve chamber58 in which an auxiliary valve 57 in the form of a plate member isoperatively mounted as shown in FIG. 4.

The valve 56 is formed at its left-hand portion with an opening 60 whichmay be closed by the auxiliary valve 57 when the latter is moved to theleft. The auxiliary valve chamber 58 is formed at its depth with aplurality of holes 61 communicating between the righthand portion of theauxiliary valve chamber 58 and the ventilating port 55 and thusventilating hole 68. This valve chamber 58 is also formed at a centralportion of its depth with a slight projection which permits, togetherwith a plurality of notches formed on the outer periphery of theauxiliary valve 57, the flow of air from the opening 60 to the holes 61even when the righthand surface of the auxiliary valve 57 is contactedwith the depth of said valve chamber 58 or the left-hand surface of saidprojection.

Provided at the left-hand extremity of the valve chamber 59 is anannular cushioning member 62, made of elastic material, having a throughhole at its center, said through hole being communicated with a passage69 which is in turn connected to the passage 44 formed in the wall ofthe cylinder 1 1.

However, it should be noted that the valve member 56 and accordingly thevalve chamber 59 are stepped to give an enlarged diameter portion on theside adjacent to the ventilating port 55. Therefore, it will thus beunderstood that, when the valve member 56 is moved to the right, acavity b will be formed betweenv said enlarged diameter portion of thevalve chamber 59 and a correspondingly reduced diameter portion of thevalve member 56. This cavity b is communicated with an exhaust port 65by means of a small passage 64, the both of the latter being formed in alower wall portion of the casing 54. At a lower portion of the casing 54beneath said exhaust port 65, a plurality of small holes 66 are disposedfor discharging the exhaust air from the port 65 to the atmosphere.

It should be noted that the valve casing 16 is rigidly secured at itsleft-hand side as viewed from FIG. 2 with another plate membercorresponding to the abovementioned plate member 21, but the platemember at the left-hand side of the valve casing 16 is provided with anoutlet hole communicated with the left-hand portion of the valve chamber23.

In this arrangement as hereinbefore fully described, the operation ofthe improved impact air driven tool of the present invention is asfollows.

When compressed air is supplied to the supply port 18 of the casing 16through the elbow 20 and then nipple 19, the compressed air will flow tothe annular groove 37 and then to the annular groove 38 communicatedtherewith by the reduced diameter portion 67 of the valve body 17.However, since the groove 38 is communicated to the passage 39 of whichthe other end is open to the interior of the cylinder 11, the compressedair thus supplied will cause the piston 15 to move downward.

At the same time, since the groove 37 is communicated with the limitingvalve chamber 26 by means of the passage 49 which is at this timecommunicates with the passage 48 by the reduced diameter portion 47 ofthe limiting valve 25, the other end of said passage 48 beingcommunicated to the gap 29 around the check valve 27, the samecompressed air will be introduced to said gap 29 and via passage 34directed to the throttle valve 32 formed in the plate member 21.

While the check valve 27 is normally positioned as illustrated in FIG.2, the air in the passage 34 will pass through a clearance a of thethrottle valve 32 to the passage 33 and then to the passage 31 passingthrough the check valve 27. Thereafter, the air in the passage 31 willbe introduced to the opening 24 through the passage 22 into the recessformed on the right-hand extremity of the valve member 17 in the axialdirection. However, since the throttle valve 32 provides a narrowclearance a as shown in FIG. 3, the air is somewhat slowly supplied fromthe passage 34 into the recess, and the value of pneumatic pressurewill, accordingly, slowly increase.

In addition thereto, since a passage communicating the groove 38 to thepassage 39 open to the interior of the cylinder 11 is communicated withthe passage 50 which is in turn communicated with the right-hand portionof the limiting valve chamber 26, the compressed air will also besupplied to the right-hand extremity of the valve 25 through saidpassage 50. The compressed air supplied into the interior of thecylinder 11 by means of the passage 39 will then flow into the passage46, which is in turn introduced against the left-hand extremity of thelimiting valve 25 through the passage 51. However, since the workingarea of the left-hand extremity of the limiting valve 25 is greater thanthat of the right-hand extremity thereof, the limiting valve 25 isbiased to the right even when as a result, pressure of the compressedair acts on both extremities thereof.

While in this condition, the annular groove 42 in the chamber 23 iscommunicated with the annular groove 41 by the reduced diameter portion40 of the valve member 17 and then to the atmosphere through the exhaustport 43 formed in a wall portion of the casing 16. Accordingly, it willbe clearly understood that the valve chamber 59 within the rapid exhaustvalve casing 54 is communicated to the atmosphere by means of thepassage 44 extending from the passage 69 communicated with said chamber59. Therefore, as the piston moves downward, the air contained in alower cylinder cavity defined between the lower extremity of the piston15 and the upper extemity of the chisel 14 will open the valve member 56and escape therefrom to the atmosphere through the ventilating port 55,the exhaust port 65 and then a plurality of the small holes 66. Thus,the piston 15 is rapidly moved downward to abut against the upperextremity of the chisel 14.

As a value of pneumatic pressure in the recess at the right-handextremity of the valve body 17 gradually increases in excess of a valueof pneumatic pressure acting on an annular area on the left-hand side ofthe enlarged diameter portion 35 so as to move the valve body 17 to theright, the valve body 17 commences to move to the left. As soon as theright-hand extemity of the valve body 17 thus passes through an O-ringprovided to the right of the annular groove 36, the valve body will berapidly moved to the left because pneumatic pressure that has beenapplied to the annular groove 36 is added to the pneumatic pressureapplied through the opening 24.

Upon completion of the movement of the valve body 17 to the left, thegrooves 37 and 42 in the valve chamber 23 are communicated to each otherby the reduced diameter portion 67 while communication between thegrooves 37 and 38 and communication between the grooves 41 and 42 arerespectively cut off. Accordingly, the compressed air supplied to thesupply port 18 will flow to the passage 44 through the groove 37and thenthe groove 42, pressing the valve member 56 and the auxiliary valve 57to the right and passing through the notches on the periphery of theauxiliary valve 57 and then the holes in the depth of the auxiliaryvalve chamber 58, and finally be supplied through the ventilating hole68 by means of the ventilating port 55 into the lower cylinder cavitydefined by the lower extremity of the piston and the upper extremity ofthe chisel. A seal ring provided in the peripheral surface of theright-hand end of the valve member 56 is at this time tightly contactedto the adjacent end surface of the ventilating port 55 so as to preventthe air in the ventilating port from leaking out.

At the same time as hereinbefore described, the grooves 41 and 45 in thevalve chamber 23 are also communicated to each other by the reduceddiameter portion 40, permitting the passage 46 to communicate with theexhaust port 43 and then to atmosphere through said grooves 41 and 45.Accordingly, the air contained in an upper cylinder cavity definedbetween the upper extremity of the piston 15 and the back of the topplate 12 will be discharged to the atmosphere through the passage 46that has been communicated with the exhaust port 43. Thus, the piston 15commences to move upward.

In addition, when the groove 45 is communicated to the atmosphere, thepassage 51 is also communicated to the atmosphere. At this time, a valueof pressure in the passage 39 and thus a valve of pressure in thepassage communicated therewith are equalized to the atmosphere. Thus,the limiting valve 25 remains to the right.

However, as the piston 15 moves upward and sub sequently its upperextremity closes the passage 46, the

remaining air in the upper cylinder cavity will be compressed andsubsequently pressure of said compressed air be applied through thepassage 50 to the right-hand extremity of the limiting valve 25 to movethe latter to the left.

As the limiting valve 25 moves to the left, the passage 48 iscommunicated by the reduced diameter portion 47 of the valve 25 with thepassage 52, permitting the air in the gap 29 and the groove 36 to bedischarged to the atmosphere therethrough by means of the exhaust port53.

Thus, as a valueof pressure within the gap 29 and the annular groove 36is equalized to the atmosphere, a value of pressure within theright-hand portion of the valve chamber 23 also reaches atmospheric and,therefore, the valve body 17 is moved to the right by the ac tion ofpressure acting on the left-hand extremity of said enlarged diameterportion 35. As soon as the lefthand extremity passes through an O-ringprovided to the right of the groove 36, communication between the groove36 and the right-hand portion of the valve chamber 23 will be cut offwith subsequent increase of a value of pressure within said right-handportion of the valve chamber 23, the increased pressure then actingthrough the passage 31 to the check valve 27 so as to open the latter.As the check valve 27 is thus opened, the air within the right-handportion of the chamber 23 can be discharged from the exhaust port 53 inthe order through the passage 22, passage 31, gap 29, passage 48 andfinally the passage 52, and, thus, the movement of the valve body 17 tothe right completes to establish the condition as shown in F l6. 2.

As a result, compressed air is again supplied into the upper cylindercavity while the passage 44 is communicated to the atmosphere.

Accordingly, it will be clearly understood that the valve chamber 59within the rapid exhaust valve casing 54 is again communicated to theatmosphere by means of the passage 44 extending from the passage 69communicated with said chamber 59. Then, in the same manner as has beenseen during the previous downward movement of the piston 15 within thecylinder 11, the air contained in the lower cylinder cavity will againopen the valve member 56 and escape therefrom to the atmosphere throughthe ventilating port 55, the exhaust port 65 and finally the small holes66, while the piston 15 is again abutted against the upper extremity ofthe chisel 14.

Subsequently, as the upper extremity of the piston 15 clears the openingof the passage 46 during its downward movement, the compressed airsupplied through the passage 39 into the upper cylinder cavity willagain flow to the passage 51 by means of the passage 46, applying itspneumatic pressure to the lefthand extremity of the limiting valve 25thereby to move the latter to the right. Thus, the limiting valve 25 canbe positioned as illustrated in FIG. 2.

As hereinbefore fully described, so long as compressed air is suppliedto the supply port 18 of the improved impact air driven tool of thepresent invention, the above-mentioned operation of one cycle may berepeated, wherein the piston is fiercely reciprocated within thecylinder to strike on the upper extremity of the chisel and thereby toperform the intended work.

According to the preferred embodiment of the present invention as shownin FIG. 1 through FIG. 4, by adjusting the opening, or a value of theclearance a, of the throttle valve 32, the number of piston strokes perunit time can be varied as desired. Even in the event that the number ofpiston strokes per unit time is varied, a value of striking energy perpiston stroke does not vary at all. The reason therefor will behereinafter set forth.

It should be noted that the piston 15 within the cylinder 1 1 has astriking phase wherein the valve body 17 and the limiting valve 25 arepositioned as shown in FIG. 2, a resting phase which continues from thetime at which the piston strikes the chisel 14 until the time at whichthe piston commences its upward movement away from the chisel, and areturn phase wherein the upward movement of the piston takes place.However, the resting phase is a time duration of the valve body 17moving from the right to the left within its valve chamber 23,commencing at the moment that the piston 15 strikes the chisel 14 andending at the moment that the piston 15 commences its upward movementaway from the chisel.

Accordingly, if the throttle valve 32 is constructed in the form ofscrew type needle valve as substantially shown in FIG. 3, a value ofpneumatic pressure acting on the right-hand extremity of the valve body17 can be rapidly increased by adjusting the valve 32 so as to increasea value of the clearance a, resulting in the reduction of the timenecessary for the valve body 17 to complete its movement from the rightto the left, that is to say, duration of the resting phase.

On the contrary, if the throttle valve 32 is adjusted so as to reducethe value of said clearance a, the duration of the resting phase may beprolonged.

As hereinbefore described, change of the duration of the resting phaseresults in the change of the number of piston strokes per unit time. Itwill be thus understood that the adjustment of the throttle valve merelyaffects the duration of the resting phase independent of the strikingphase and the return phase. Therefore, the number of the piston strokesper unit time can be advantageously adjusted without any substantialreduction of the amount of the striking energy obtained by the improvedimpact air driven tool of the present invention.

Referring now to FIG. through FIG. 9 in which a modified embodiment ofthe present invention is shown, reference numeral 71 represents acylinder, 72 represents a top plate secured to an upper end of saidcylinder, 73 represents a chisel holder, 74 represents a chisel, and 75represents a piston slidably received in said cylinder.

Reference numeral 76 represents a valve casin secured to a lateral upperportion of said cylinder 71, in which valve casing a valve body 77 isslidably received. This valve casing 76 is formed with a compressed airsupply port 78 to which a nipple 79 is pivotably connected. One end ofsaid nipple 79 remote from said port 78 is rigidly connected with anelbow 80 to which a tubular hose connected from a suitable compressormeans may be connected. The valve casing 76 is secured at its bothright-hand and left-hand sides as viewed from FIG. 6 with a pair ofplate members 81 and 92, one of which or the right-hand plate member 81being formed therein with a passage 82 communicated with an opening 84of a valve chamber 83 in which said valve body 77 is slidably received.

The valve casing 76 is also provided therein with a time lag valvechamber 86 in which a time lag valve 85 is slidably received and with avalve chamber 88 in which a check valve 87 is provided. Provided aroundthe outer periphery of said valve chamber 88 is an annular gap 89. Thechambers 88 and 86 are connected to each other by a passage 91. Thecheck valve 87 is normally biased to the right within its valve chamber88 so as to permit the flow of air from the passage 91 to the gap 89,but to restrict the flow of air from the gap 89 to the passage 91.

The other or left-hand plate member 92 is provided therein with athrottle valve 93 in the form, for example, of an adjustable needlevalve and at a suitable position with an exhaust hole communicatingbetween the left-hand portion of the chamber 83 and the atmosphere.

The throttle valve 93 is positioned between a passage 94 communicatedwith the valve chamber 88 and a passage 95 communicated with the gap 89,so as to act to regulate the flow of air therebetween.

The valve body 77 is formed at its intermediate portion with a reduceddiameter portions 103 and 140 and at its right-hand end with an enlargeddiameter portion 96 which is in turn formed at its right-hand extremitywith a circular recess in the axial direction thereof. The valve chamber83 is provided on its inner peripheral surface with annular grooves 97and 98 which can be isolated from each other by the enlarged diameterportion 96 as the valve body 77 is moved to the left, said passage 98being in turn connected with a passage 99 open to the interior of thecylinder 71 and said passage 97 being in turn connected with the supplyport 78.

This valve chamber 83 is also formed on a left-hand inner peripheralsurface with a plurality of annular grooves 100, 101 and 102, thegrooves 100 and 101 being communicated to each other by the reduceddiameter portion 103 of the valve body 77 when the latter is moved tothe left while the grooves 101 and 102 being communicated to each otherby said reduced diameter portion of the valve body 77 when the latter ismoved to the right. The groove 100 is in turn connected with a passage104 open to the interior of the cylinder 71 at a position below theopening of the passage 99 formed on the inner peripheral surface of thecylinder 71, the groove 101 is in turn connected with an exhaust port105 formed in the casing 76 and the groove 102 is in turn connected witha passage 106 formed in a wall portion of the cylinder 71.

The time lag valve 85 is formed at its intermediate portion with areduced diameter portion 107 which, upon movement of said valve 85 tothe left, acts to communicate between passages 108 and 109 formed on theinner peripheral surface of the valve chamber 86. The passage 108 isdirectly connected with an exhaust port 110. To the left of said passage108, a passage 111 communicating between the valve chamber 86 and apassage 112 which is in turn connected to a passage 95 formed in theplate member 92.

The valve chamber 86 is also formed at its right-hand portion with apassage 1 13 connected to the groove 97, the right-hand portion 114 ofthe chamber 86 being also connected to said groove 97. The right-handportion 114 is designed to slidably receive a right-hand reduceddiameter portion 115 of the time lag valve 85 therein, the diameter ofsaid reduced diameter portion 115 being smaller than that of theleft-hand extremity of the valve body 85. The right-hand portion isprovided on its left-hand inner peripheral surface with an O-ring, tothe left of which O-ring the valve chamber 86 is somewhat enlarged togive its diameter greater than that of the right-hand portion 114. Aboutthe boundary between said portion 114 and that enlarged portion of thevalve chamber 86, an exhaust hole communicating between that enlargedportion of the chamber 86 to the atmosphere is provided.

The cylinder 71 is provided on its inner peripheral surface at aposition below the opening of the passage 104 formed thereon withanother opening in which a limiting valve operating member 116 iscollapsibly mounted in such a manner as to project a portion thereoftoward the interior of the cylinder 71 unless the projected portion 'isbackwardly retracted by the piston 75. This operating member 116 is inthe form of a ball and, as shown in FIG. 9, acts to operate a limitingvalve 118 in a valve chamber 117 formed within a limiting valve casing145 formed in the cylinder wall. The limiting valve 118 is normallybiased toward the operating member 116 by a spring 119 and will operatewhen the operating member 116 is collapsed by the piston 75.

The valve chamber 117 is formed about its outer periphery with a passage120 communicated with the passages 111 and 112 within the valve casing76 and the passage 95 in the plate member 92 by means of an annularcavity 121 formed in said valve casing 117.

This valve chamber 117 is also formed at its depth with a valve seat 122to which the limiting valve 118 is seated by the spring 119. Providedaround said valve seat 122 is a passage 123 communicated with an exhaustport 125, formed in the valve casing 76, through a passage 124 formed inthe cylinder wall. Provided adjacent to the left-hand extremity of thelimiting valve 118 is a cavity 141 formed in the valve casing 76 incommunication with the annular groove 97 within the valve chamber 83 bymeans of a passage 146. The limiting valve 118 is also formed at itsleft-hand extremity with a recess 142 of a desired depth incommunication with a passage 143 which is in turn connected with theannular cavity 121 by means of a passage 144, the both passages 143 and144 being formed within the valve casing 145 at a position adjacent tothe left-hand exv tremity of the limiting valve 118.

Reference numeral 126 represents a rapid exhaust valve casing secured tothe cylinder 71. As shown particularly in FIG. 8, this rapid exhaustvalve casing 126 is formed with a ventilating port 127 directlycommunicated with a ventilating hole 146 formed in the wall of thecylinder 71. Within said valve casing 126, a valve chamber 129 is formedfor slidably receiving therein a valve member 128 capable of closing andopening the ventilating port 127. The valve member 128 is formed with anauxiliary valve chamber 130 in which an auxiliary valve 131 in the formof a plate member is operatively mounted.

The valve member 128 is formed at its left-hand por tion with an opening132 which may be closed by the auxiliary valve 131 when the latter ismoved to the left.

The auxiliary valve chamber is formed at its depth with a plurality ofholes 133 communicating between the right-hand portion of the auxiliaryvalve chamber 130 and the ventilating port 127 and thus the ventilatinghole 146. This valve chamber 129 is also formed at a central portion ofits depth with a slight projection which permits, together with a.plurality of notches formed on the outer periphery of the auxiliaryvalve 131, the flow of air from the opening 132 to the holes 133 evenwhen the right-hand surface of the auxiliary valve 131 is contacted withthe depth of said valve chamber 129 or the left-hand surface of saidprojection.

Provided at the left-hand extremity of the valve chamber 129 is anannular cushioning member 134, made of elastic material, having athrough hole at its center, said through hole being communicated with apassage 135 which isin turn connected to the passage 106 formed in thewall of the cylinder 71.

However, it should be noted that the valve member 128 and accordinglythe valve chamber 129 are stepped to give an enlarged diameter portionon the side adjacent to the ventilating port 127. Therefore, it willthus be understood that, when the valve member 128 is moved to theright, a cavity d will be formed between said enlarged diameter portionof the valve chamber 129 and a correspondingly reduced diameter portionof the valve member 128. This cavity d is communicated with an exhaustport. 138 by means of a small passage 137, the both of the latter beingformed in a lower wall portion of the casing 126. At a lower portion ofthe casing 126 beneath said, exhaust port 138, a plurality of smallholes 139 are disposed for discharging the exhaust air from the port 139to the atmosphere.

While in the arrangement of the modified embodiment of the presentinvention as hereinbefore fully described, the improved impact airdriven tool according thereto may function in such a manner ashereinafter set forth.

When compressed air is supplied to the supply port 78 of the casing 76through the elbow 80 and then nipple 79, the compressed air will flow tothe annular groove 97 and then to the annular groove 98 communicatedtherewith by the reduced diameter portion 140 of the valve body 77.However, since the groove 98 is communicated to the passage 99 of whichthe other end is open to the interior of the cylinder 71 at a positionabove the upper extremity of the piston 75, the compressed air thussupplied will cause the piston 75 to move downward.

At the same time, the annular groove 102 connected to the passage 135 ofthe rapid exhaust valve casing 126 by means of the passage 106 iscommunicated by the reduced diameter portion 103 of the valve body 77with the annular groove 101 communicated in turn to the exhaust port105. Accordingly, it will be clearly un derstood that, as the piston 75is downwardly moved, the air contained in a lower cylinder cavitydefined between the lowermost end surface of said piston and theuppermost end surface of the chisel 74 will press the valve member 128whereby said air can be discharged to the atmosphere through the exhaustport 138 and then the holes 139, resulting in the rapid downwardmovement of the piston to strike the chisel 74.

The annular groove 97 is then communicated with the right-hand portion 114 of the valve chamber 86 and the groove 1 13 which is in turncommunicated with the time lag valve chamber 215. Accordingly, thecompressed air will also act on the right-hand reduced diameter portion115 of the time lag valve 85 to render the valve 85 to move to the leftand thereby to close the passage 113, as shown in FIG. 6. In addition,since the groove 97 is communicated with the cavity 141 of the limitingvalve casing by means of the passage 146, the pneumatic pressure willalso act on the left-hand extremity of the valve 118 and then flow tothe annular cavity 121 in the order through the recess 142, passage 143and passage 144. Then, the air in the annular cavity 121 then in partflow to the passage 95 in the plate member 92 and thus to the passage 94through a clearance c of the throttle valve 93. The air in the passage94 is introduced against the left-hand extremity of the time lag valve85 through the check valve 87 by means of the passage 91. Also, thecompressed air in the passage 85 will in part flow into the gap 89,acting on the check valve 87.

Accordingly, the compressed air is slowly accumulated within a left-handportion of the valve chamber 88 and the passage 91 via the clearance cof the throttle valve.

Although the compressed air acts on the both extremities of the time lagvalve 85 as hereinbefore described, the time lag valve 85 is positionedto the left until a value of pressure of the compressed air acting onthe left-hand extremity of the valve 85 increases over that of pressureacting on the right-hand reduced diameter portion 115 of said valve.Upon increase of the value of pressure acting so as to move the valve 85to the right in excess of the value of pressure acting so as to move thevalve 85 to the left, the valve 85 commences to move to the right. Assoon as the left-hand extremity of the valve 85 passes through theO-ring positioned at the left side of the valve chamber 86, it can berapidly moved to the right as pressure in the passage 112 is alsoapplied through the passage 111 to the left-hand extremity thereof,until the right-hand reduced diameter portion 115 is abutted against thecushioning member provided at the depth of the righthand portion 1 14 ofthe chamber.

As the time lag valve 85 is thus moved to the right, the reduceddiameter portion 107 of said valve communicates the passage 109 with thepassage 113. However, it should be noted that the compressed air fromthe groove 97 always exists in the passage 113 throughout the operationof the impact air driven tool of the present invention. Therefore, uponcommunication between the passages 109 and 113, the air flows into thepassage 109 from the passage 113 and the to the right-hand portion ofthe chamber 83 through the opening 84 by means of the passage 82communicated therewith. This air thus supplied then acts on therighthand extremity of the enlarged diameter portion 96 of the valvebody 77 so as to move the latter to the left.

As the valve body 77 is moved to the left, the reduced diameter portionof the valve 77 communicates the groove 101 with the groove 100 while anintermediate portion of said valve 77 isolates the grooves 101 and 102and the reduced diameter portion 140 of the valve 77 communicates thegroove 97 with the groove 102 while the enlarged diameter portion 96thereof closes the groove 98. Subsequently, the air in the groove 97 issupplied to the passage 106 through the groove 102 and then to thepassage 135, then passing through the notches on the periphery of theauxiliary valve 131 and then the ventilating port 127 into the lowercylinder cavity defined between the lowermost end of the piston and theuppermost end of the chisel. Thus, it will be understood that the pistonis upwardly moved thereby. At this time, the seal ring provided in theperipheral surface of the right-hand end of the valve member 128 istightly contacted to the adjacent end surface of the ventilating port127 so as to prevent the air in the ventilating port from leaking out.

While in this condition as hereinbefore described, the air contained inthe upper cylinder cavity is discharged to the atmosphere in the orderthrough the passage 104, the grooves 100 and 101 communicated to eachother, and the exhaust port 105 of the casing 76.

However, as the piston 75 is upwardly moved a sufficient distance, thelimit valve operating member 116 is backwardly retracted by theuppermost end of said piston. Rectraction of said member 116 will causethe limit valve 118 to move to the left, compressing the spring 119while closing the passage 143 in the valve 118. At this time, thepassage 124 communicated to the atmosphere commences to communicate withthe valve chamber 1 17. However, since this valve chamber 117 iscommunicated with the left-hand portion of the valve chamber 86 throughthe passage 120, the annular groove 121, and the passages 112 and 111,the air in said portion of the valve chamber 86 is exhausted and thetime lag valve 85 is moved to the left under the influence of thepneumatic pressure always existing in the right-hand portion 114 assupplied from the groove 97. Also, upon communication of the passage 112with the exhaust port 125, the air in the passage 95 and the gap 89 isexhausted while the air contained in the check valve 87 and the passage91 presses the check valve 87 so as to open the latter so that this airis also exhausted through the exhaust port 125 by means of the gap 89.

Thus, when the time lag valve 85 is moved to the left as hereinbeforedescribed, the passages 108 and 109 are communicated to each other andthe air contained in the right-hand portion of the valve chamber 83 canbe discharged to the atmosphere via the opening 84,

the passage 82 and then through the exhaust port. Ac-

cordingly, the valve body 77 is returned to the right with its enlargeddiameter portion 96 being applied with pneumatic pressure in theleft-hand portion of the valve chamber 83, thus commencing the nextcycle of operation.

As hereinbefore fully described, so long as compressed air is suppliedto the supply port 78 of the improved impact air driven tool of thepresent invention, the above-mentioned cycle of its operation may berepeated, wherein the piston 75 is fiercely reciprocated within thecylinder to strike on the upper extremity of the chisel 74 and therebyto perform the intended work.

Even in the modified embodiment of the impact air driven tool of thepresent invention, the number of piston strokes per unit time can bevaried by adjusting the opening, or the value of the clearance c, of thethrottle valve 93 as in the first mentioned embodiment of the presentinvention. Similarly, even in the event that the number of pistonstrokes per unit time is varied, the value of striking energy per pistonstroke does not vary at all.

More particularly, it should be noted that the piston 75 within thecylinder 71 has a striking phase, a resting phase and a return phasethroughout each cycle of operation. However, according to the modifiedembodiment of the present invention, by adjusting the duration of theresting phase of the piston, the number of piston strokes per unit timecan be varied without affecting the striking phase and the return phase.

In other words, the resting phase of the piston 75 represents a durationof time between the time at which the piston strikes the chisel and thetime-at which said piston commences its upward movement away from saidchisel. However, this time duration may be determined by the timenecessary for the time lag valve 85 to complete its movement to theright after the piston strikes the chisel.

In order to cause the time lag valve 85 to move from the left to theright, it is necessary to increase the value of pneumatic pressureacting through the clearance c of the throttle valve 93 on the left-handextremity of said valve 85. Accordingly, it will be clearly understoodthat the time necessary for the time lag valve 85 to complete itsmovement to the right after the piston strikes the chisel can be variedby adjusting the size of the clearance c and thereby to adjust the rateof increase of the pneumatic pressure acting therethrough on thelefthand extremity of said time lag valve 85.

Accordingly, if the throttle valve 73 is constructed in the form ofscrew type needle valve as substantially shown in FIG. 7 in order topermit the adjustment of the size of the clearance c, the number ofpiston strokes per unit time can be varied through controlling theduration of the resting phase of the piston.

, In addition thereto, in the modified embodiment of the presentinvention, the impact air driven tool is designed such that the limitingvalve 118 is actuated to bring the time lag valve 85 into the strikingphase during the return movement of the piston 75 away from the chisel74 and thereby to bring the valve body 77 into the striking phasethrough the shifting movement of said valve 85. Therefore, retardationof the shifting movement of the valve body 77 with respect to themovement of the piston 75 does not take place with smooth, rapid shiftof the movement of the piston from the return phase to the strikingphase.

What I claim is:

1. An air driven impact tool comprising a cylinder with a closed upperend, a chisel closing the bottom end of said cylinder, an impact pistonmovable within said cylinder and forming an upper cavity between saidpiston and said upper end and a lower cavity between said piston andsaid chisel; a casing attached to said cylinder at the upper portionthereof, a main valve body movably mounted in said casing, a limitingvalve movably mounted in said casing, an adjustable throttle valvemounted within said casing, a one-way check valve movably mounted insaid case, a compressed air supply port extending into said casing andacting to bias said main valve body in a first direction, a firstpassage communicating said compressed air to said upper cavi ty whatsaid main valve bodyjs in said first djrecti n, a secon passagecommunicating compresse air rom said upper cavity to urge said limitingvalve in a given direction; an exhaust valve connected to said cylinderbelow said casing, an opening communicating said exhaust valve to saidlower cavity, a third passage from said casing to said exhaust valvecommunicating said lower cavity to atmosphere when said main valve bodyis in said first direction; said piston being forced downwardly tostrike said chisel when said compressed air is supplied to said uppercavity; a channel through said adjustable throttle valve to slowlysupply said compressed air to bias said main valve body in a directionopposite said first direction, whereby a predetermined time after saidpiston strikes said chisel said main valve body is moved in saidopposite direction, said first passage being blocked from communicationwith said compressed air and exhausted to atmosphere when said mainvalve body is in said opposite direction, and said third passage beingconnected to said compressed air supply when said main valve body is insaid opposite direction such that compressed air is supplied to saidlower cavity.

2. An air driven impact tool comprising a cylinder with a closed upperend, a chisel closingthe bottom end of said cylinder, an impact pistonmovable within said cylinder and forming an upper cavity between saidpiston and said upper end and a lower cavity between said piston andsaid chisel; a casing attached to said cylinder at the upper portionthereof, a main valve body movably mounted in said casing, time lagvalve movably mounted in said casing, a one-way check valve movablymounted in said casing, an adjustable throttle valve mounted within saidcasing, a limitvalve operating member mounted within said casing andhaving a member extending into said upper cavity, a compressed airsupply port extending into said casing and acting to bias said mainvalve body in a first direction, a first passage communicating saidcompressed air to said upper cavity when said main valve body is in saidfirst direction; an exhaust valve connected to said cylinder below saidcasing, an opening communicating said exhaust valve to said lowercavity, a second passage from said casing to said exhaust valvecommunicating said lower cavity to atmosphere when said main valve bodyis in said first direction; said piston being forced downwardly tostrike said chisel when said compressed air is supplied to said uppercavity; a channel through said adjustable throttle valve to slowlysupply said compressed air to urge said time lag valve in a givendirection, whereby a predetermined time after said piston strikes saidchisel said tine lag valve and said main valve body are moved indirections opposite to said given direction and first direction,respectively, said first passage being blocked from communication withsaid compressed air and exhausted to atmosphere when said main valvebody is in said opposite direction, said second passage being connectedto said compressed air supply when said time lag valve is in saidopposite direction such that compressed air is supplied to said lowercavity, and said member of said limit valve operating member beingmovable upon contact by said piston when said piston moves upwardly.

1. An air driven impact tool comprising a cylinder with a closed upperend, a chisel closing the bottom end of said cylinder, an impact pistonmovable within said cylinder and forming an upper cavity between saidpiston and said upper end and a lower cavity between said piston andsaid chisel; a casing attached to said cylinder at the upper portionthereof, a main valve body movably mounted in said casing, a limitingvalve movably mounted in said casing, an adjustable throttle valvemounted within said casing, a one-way check valve movably mounted insaid case, a compressed air supply port extending into said casing andacting to bias said main valve body in a first direction, a firstpassage communicating said compressed air to said upper cavity when saidmain valve body is in said first direction, a second passagecommunicating compressed air from said upper cavity to urge saidlimiting valve in a given direction; an exhaust valve connected to saidcylinder below said casing, an opening communicating said exhaust valveto said lower cavity, a third passage from said casing to said exhaustvalve communicating said lower cavity to atmosphere when said main valvebody is in said first direction; said piston being forced downwardly tostrike said chisel when said compressed air is supplied to said uppercavity; a channel through said adjustable throttle valve to slowlysupply said compressed air to bias said main valve body in a directionopposite said first direction, whereby a predetermined time after saidpiston strikes said chisel said main valve body is moved in saidopposite direction, said first passage being blocked from communicationwith said compressed air and exhausted to atmosphere when said mainvalve body is in said opposite direction, and said third passage beingconnected to said compressed air supply when said main valve body is insaid opposite direction such that compressed air is supplied to saidlower cavity.
 2. An air driven impact tool comprising a cylinder with aclosed upper end, a chisel closing the bottom end of said cylinder, animpact piston movable within said cylinder and forming an upper cavitybetween said piston and said upper end and a lower cavity between saidpiston and said chisel; a casing attached to said cylinder at the upperportion thereof, a main valve body movably mounted in said casing, timelag valve movably mounted in said casing, a one-way check valve movablymounted in said casing, an adjustable throttle valve mounted within saidcasing, a limit valve operating member mounted within said casing andhaving a member extending into said upper cavity, a compressed airsupply port extending into said casing and acting to bias said mainvalve body in a first direction, a first passage communicating saidcompressed air to said upper cavity when said main valve body is in saidfirst direction; an exhaust valve connected to said cylinder below saidcasing, an opening communicating said exhaust valve to said lowercavity, a second passage from said casing to said exhaust valvecommunicating said lower cavity to atmosphere when said main valve bodyis in said first direction; said piston being forced downwardly tostrike said chisel when said compressed air is supplied to said uppercavity; a channel through said adjustable throttle valve to slowlysupply said compressed air to urge said time lag valve in a givendirection, whereby a predetermined time after said piston strikes saidchisel said tine lag valve and said main valve body are moved indirections opposite to said given direction and first direction,respectively, said first passage being blocked from communication withsaid compressed air and exhausted to atmosphere when sAid main valvebody is in said opposite direction, said second passage being connectedto said compressed air supply when said time lag valve is in saidopposite direction such that compressed air is supplied to said lowercavity, and said member of said limit valve operating member beingmovable upon contact by said piston when said piston moves upwardly.